Before this patch there was only partial support for ANDQconst
which was not lowered. This patch added support for AND operations
for all bit sizes and signs.

Change-Id: I3a6b2cddfac5361b27e85fcd97f7f3537ebfbcb6
Reviewed-on: https://go-review.googlesource.com/12761Reviewed-by: Keith Randall <khr@golang.org>